1. Field of the Invention
The present invention relates to a jet-propulsive watercraft which ejects water rearward and planes on a water surface as the resulting reaction. More particularly, the present invention relates to a jet-propulsive watercraft that can maintain steering capability even when the throttle is operated to be closed and propulsive force is thereby reduced.
2. Description of the Related Art
In recent years, so-called jet-propulsive personal watercrafts (PWC) have been widely used in leisure, sport, rescue activities, and the like. The personal watercraft is configured to have a water jet pump that pressurizes and accelerates water sucked from a water intake generally provided on a bottom of a hull and ejects it rearward from an outlet port. Thereby, the personal watercraft is propelled.
In the personal watercraft, in association with a steering handle of a general bar type, a steering nozzle provided behind the outlet port of the water jet pump is swung rightward or leftward, to change the ejecting direction of the water to the right or to the left. Thereby, the watercraft is turned to the right or to the left.
A deflector is retractably provided behind the steering nozzle for blocking the water ejected from the steering nozzle from above. The deflector is moved downward to deflect the ejected water forward, and as the resulting reaction, the personal watercraft moves rearward. In some watercraft, in order to move rearward, a water flow is formed from an opening provided laterally of the deflector along a transom board to reduce the water pressure in an area behind the watercraft.
Accordingly, in the above-described personal watercraft, when the throttle is moved to a substantially fully closed position and the water ejected from the water jet pump is thereby reduced, during forward movement and rearward movement, the propulsive force necessary for turning the watercraft is correspondingly reduced, and the steering capability of the watercraft is therefore reduced until the throttle is re-opened.
To solve the above-described problem with a mechanical structure, the applicant disclosed a jet-propulsive personal watercraft comprising a steering component for an auxiliary steering system which operates in association with the steering handle in addition to a steering nozzle for the main steering system in Japanese Patent Application No. Hei. 2000-6708.
The present invention has been developed for obviating the above-described problem, and an object of the present invention is to provide a jet-propulsive watercraft that can maintain steering capability in a way adapted to forward movement and rearward movement of the watercraft even when the operation for closing a throttle (defined as operation causing at least a part of a descending line Zb of FIG. 11 and hereinafter referred to as xe2x80x9cthrottle-close operationxe2x80x9d) is performed and the amount of water ejected from a water jet pump is thereby reduced.
According to the present invention, there is provided a jet-propulsive watercraft comprising: a water jet pump that pressurizes and accelerates sucked water and ejects the water from an outlet port provided behind the water jet pump to propel the watercraft as a reaction of the ejecting water; an engine for driving the water jet pump; a steering operation means that operates in association with a steering nozzle of the water jet pump; a steering position sensor for detecting a predetermined steering position of the steering operation means; and an electric control unit, wherein the electric control unit is adapted to temporarily increase the speed of the engine when a result detected by the steering position sensor is the predetermined steering position.
According to the jet-propulsive watercraft of the present invention, the engine speed is temporarily increased when the steering operation means is operated and this operation is detected by the steering position sensor. Therefore, the water sufficient to turn the watercraft is ejected from the water jet pump, and the steering capability can be maintained even when the throttle-close operation is performed.
Herein, control for temporarily increasing the engine speed is referred to as xe2x80x9csteering assist mode controlxe2x80x9d, and the xe2x80x9cthrottle-close operationxe2x80x9d means that operation is performed to bring the throttle toward a closed position by a predetermined amount or more.
The jet-propulsive watercraft may further comprise a throttle-close operation sensor for detecting throttle-close operation, and the engine speed is temporarily increased when the steering operation is detected by the steering position sensor and the throttle-close operation is detected by the throttle-close operation sensor.
The jet-propulsive watercraft may further comprise an engine speed sensor for detecting an engine speed of the engine, and the engine speed is temporarily increased when the steering operation is detected by the steering position sensor and a result detected by the engine speed sensor is not larger than a first predetermined engine speed.
In this case, when the engine speed becomes the predetermined engine speed or less after the throttle-close operation, transition to the steering assist mode control takes place. Therefore, the steering assist mode control can be effectively started when the water ejected from the water jet pump becomes insufficient to turn the watercraft, regardless of the speed of the watercraft at a point of the throttle-close operation. Also, the engine speed can be temporarily increased when a result detected by the engine speed sensor is not smaller than a second predetermined engine speed.
In the jet-propulsive watercraft, the throttle-close operation may be detected by a throttle position sensor.
It should be noted that the throttle-close operation sensor of the present invention is not limited to the engine speed sensor and the throttle position sensor. For example, it is possible to use a sensor placed in a system connecting a throttle lever and a throttle valve for detecting operation of the system when the throttle-close operation is performed. Also, it is possible to use a sensor for detecting an air-intake pressure and an air-intake amount of the engine. When the air-intake pressure is employed, the relationship between the air-intake pressure and the engine speed is obtained in advance, and according to this relationship, the throttle-close operation is detected only when the engine speed is low.
Under the steering assist mode control, the engine speed can be increased by changing at least any of a fuel injection timing of a fuel injection system of the engine, an ignition timing of an ignition system of the engine, and a fuel injection amount of the fuel injection system of the engine. In this case, the engine speed can be increased without actual operation of the throttle.
It is preferable that the engine speed is increased up to approximately 2500 rpm-3500 rpm as an upper limit under the steering assist mode control.
The jet-propulsive watercraft may further comprise: a speed sensor, and the engine speed can be temporarily increased when the steering operation is detected by the steering position sensor and a result detected by the speed sensor is not larger than a predetermined speed. The speed sensor may comprise an engine speed sensor, a cruising speed sensor, or the like.
It is preferable that the steering assist mode control is not executed particularly when the engine speed is within an idling range while the watercraft is moving forward because this is unnecessary. The idling range is defined as the range from the idling speed to a speed slightly higher than the idling speed and is preferably below approximately 2500 rpm.
The steering assist mode control may be executed even when the watercraft is moving rearward. In this case, it is preferable that the control is executed even when the engine speed is within the idling range.
The above-described steering assist mode control is terminated at any of the following conditions, such as when the steering operation and/or the throttle-close operation is not detected any more, and/or when the detected engine speed or the detected cruising speed is not larger than for example, a relatively low predetermined speed (second predetermined speed) any more, and/or when the detected engine speed or the detected cruising speed is not larger than the second predetermined speed any more or not smaller than for example, a relatively high predetermined speed (first predetermined speed) any more, accordingly the activation of the control should be maintained until any of the above conditions is detected. These conditions can be set for either forward movement or rearward movement of the watercraft. However, the conditions different from the conditions for forward movement can also be set for the rearward movement.
The above and further objects and features of the invention will more fully be apparent from the following detailed description with accompanying drawings.